1. Field of the Invention
The present invention relates to a UWB (UWB: Ultra Wide Band) repeater for relaying pulse signals of UWB, and a UWB communication system for carrying out bi-directional communications using UWB pulse signals.
2. Description of the Related Art
A UWB wave for carrying out radio communications by radiating steep pulse waveforms in free air has attempted to be used in micro wave bands not only for radio communications but also for measuring with radar, etc. As for the frequency of this communication system, the ratio of the bandwidth to the center frequency (that is, used bandwidth/center frequency) is 20% or more, and a remarkably wide bandwidth is utilized in comparison to a case where the ratio of the bandwidth is several percent even in general wide-band radio communication system.
FIG. 7 is a view showing one example of UWB pulse waveforms. When viewing the waveform in timebase, a pulse for transmitting data is steep, and a specified time elapses until the next pulse comes. That is, a pulse series as shown in FIG. 7 is brought about. Thus, it is possible to transmit information containing several bits by the existence and phase of one pulse. In FIG. 7, t1 and t2 indicate the times when a pulse appears. T1 indicates a pulse width.
This results in a frequency band of several GHz where the ratio of the bandwidth in the micro waveband is 20% or more. Although there is a possibility that communications and radar, which have been used conventionally, are subjected to interference by UWB in a bandwidth, other communications are carried out in a narrow bandwidth in comparison to the bandwidth of UWB, wherein it is possible to alleviate influences of UWB by a filter. Although the influences of UWB can be alleviated by a filter, the transmission power of UWB is suppressed to a low level in order to protect existing communications, a transmission range of only several tens of meters can be obtained even in free space.
Because the UWB is a wide bandwidth, although the above-described problems exist, the UWB can handle transmissions whose data rate is 100 Mbps or more. Further, the receiver of the UWB can be simplified because the UWB is not a system for modulating a carrier wave. Therefore, the UWB is in an attempt to widely prevail by virtue of the above reason.
Further, it is described in Non-Patent Document 1 that the UWB is expected as a technology for realizing high-speed radio communications.